1. Field of the Invention
The present invention relates to a method for manufacturing an optical filter having a single layer or multiple layers of dielectric material deposited on a substrate.
2. Description of the Background Art
Conventionally, a dielectric single layer film filter or dielectric multi-layer film filter formed by depositing dielectric materials on a glass substrate has been used as an optical filter for wavelength selection purpose. In such an optical filter, the transmission wavelength is made variable by varying the thickness of deposition of the dielectric material in a planar direction of the filter. Such an optical filter is manufactured by depositing the dielectric material while giving a planar distribution in the dielectric material deposition thickness at a time of depositing a dielectric film 2 on a disk shaped substrate 1 as shown in Fig. In this way, it is possible to realize an optical filter with the transmission wavelength varying with respect to an angle xcex8 (=0 to 2xcfx80) along the direction of rotation of the substrate 1. See U.S. patent application Ser. No. 09/174,724, now U.S. Pat. No. 6,157,025, for further detail.
Such an optical filter should preferably have a characteristic that the transmission wavelength varies linearly with respect to the rotation angle xcex8 of the substrate 1. In this regard, the conventional manufacturing method has employed a film formation method in which the deposition time of the dielectric material is varied linearly with respect to the angle xcex8, i.e., in the spiral shape, by using a shutter 3 that can be opened or closed like fans as shown in FIG. 2.
However, this method using the fan shaped shutter 3 of FIG. 2 inevitably leaves a region of the angle xcex8 on which no dielectric material is deposited on the substrate 1. Namely, even when the shutter 3 is fully opened, there remains a region which is continually covered by the shutter 3 as shown in FIG. 3, so that this region cannot be utilized as the optical filter. Also, in this method, it is difficult to smoothly move the shutter 3 up to a fully opened state, so that it has been impossible to deposit the dielectric material at sufficient precision. For this reason, it has been impossible to realize an optical filter in which almost the entire range of the angle xcex8 is utilizable as the optical filter.
It is therefore an object of the present invention to provide a method for manufacturing an optical filter capable of manufacturing an optical filter in such a manner that the transmission wavelength varies linearly with respect to the angle xcex8 in the rotation direction of the substrate and that almost the entire range of the angle xcex8 is utilizable as the optical filter.
According to one aspect of the present invention there is provided a method for manufacturing a disk shaped optical filter, comprising the steps of: providing a mask over a substrate, the mask being capable of being rotated relatively with respect to the substrate coaxially on a plane parallel to the substrate and the mask having an aperture extending along a radius direction with an aperture angle xcfx86; and depositing a dielectric material in a single layer or multiple layers on the substrate from the mask side within a deposition chamber, while relatively rotating the mask with respect to the substrate at least once at a non-constant angular speed during a formation of the single layer or the multiple layers on the substrate.
According to another aspect of the present invention there is provided a method for manufacturing a disk shaped optical filter, comprising the steps of: providing a mask over a substrate, the mask being capable of being rotated relatively with respect to the substrate coaxially on a plane parallel to the substrate and the mask extending along a radius direction to cover an angle xcfx86; and depositing a dielectric material in a single layer or multiple layers on the substrate from the mask side within a deposition chamber, while relatively rotating the mask with respect to the substrate at least once at a non-constant angular speed during a formation of the single layer or the multiple layers on the substrate.
Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.